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  • Seismological Society of America (SSA)  (2)
  • Geological Society (of London)  (1)
  • 1
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    Multistation Validation of Waveform Correlation Techniques as Applied to Broad Regional Monitoring (2014)
    Seismological Society of America (SSA)
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    Publication Date: 2014-12-05
    Description: Waveform correlation is garnering attention as a method for detecting, locating, and characterizing similar seismic events. To explore the opportunities for using waveform correlation in broad regional monitoring, we applied the technique to a large region of central Asia over a three-year period, monitoring for events at regional distances using three high-quality stations. We discuss methods for choosing quality templates and introduce a method for choosing correlation detection thresholds, tailored for each template, for a desired false alarm rate. Our SeisCorr software found more than 10,000 detections during the three-year period using almost 2000 templates. We discuss and evaluate three methods of confirming detections: bulletin confirmation, high correlation with a template, and multistation validation. At each station, 65%–75% of our detections could be confirmed, most by multistation validation. We confirmed over 6500 unique detections. For monitoring applications, it is of interest that a significant portion of the Comprehensive Nuclear-Test-Ban Treaty Organization’s Late Event Bulletin (LEB) catalog events was detected and that adding our confirmed detections for the LEB catalog would more than double the catalog size. Waveform correlation also allows for relative magnitude calculation, and we explore the magnitudes of detected events. The results of our study suggest that doing broad regional monitoring using historical and real-time-generated templates is feasible and will increase detection capabilities.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America (SSA)
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  • 2
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    The largest expected earthquake magnitudes in Central Asia: statistical inference from an earthquake catalogue with uncertain magnitudes (2015)
    Geological Society (of London)
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    Publication Date: 2015-11-06
    Description: The knowledge of the largest expected earthquake magnitude in a region is one of the key issues in probabilistic seismic hazard calculations and the estimation of worst-case scenarios. Earthquake catalogues are the most informative source of information for the inference of earthquake magnitudes. We analysed the earthquake catalogue for Central Asia with respect to the largest expected magnitudes m T in a pre-defined time horizon T f using a recently developed statistical methodology, extended by the explicit probabilistic consideration of magnitude errors. For this aim, we assumed broad error distributions for historical events, whereas the magnitudes of recently recorded instrumental earthquakes had smaller errors. The results indicate high probabilities for the occurrence of large events (M≥8), even in short time intervals of a few decades. The expected magnitudes relative to the assumed maximum possible magnitude are generally higher for intermediate-depth earthquakes (51–300 km) than for shallow events (0–50 km). For long future time horizons, for example, a few hundred years, earthquakes with M≥8.5 have to be taken into account, although, apart from the 1889 Chilik earthquake, it is probable that no such event occurred during the observation period of the catalogue.
    Print ISSN: 0305-8719
    Electronic ISSN: 2041-4927
    Topics: Geosciences
    Published by Geological Society (of London)
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  • 3
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    Detailed Analysis of the Far-Regional Seismic Coda in Kazakhstan Using Array Processing (2017)
    Seismological Society of America (SSA)
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    Publication Date: 2017-03-23
    Description: An analysis of seismic coda phases recorded by five small aperture arrays in Kazakhstan and Russia is performed. The characteristics of the coda phases are obtained using array processing providing estimates of direction of propagation, frequency content, and apparent propagation velocity of coherent arrivals propagating through the arrays. A statistical analysis, using the coda characteristics of the whole dataset (far-regional earthquakes) recorded by the arrays, is performed leading to a time-azimuth distribution of the detected waves. Long Lg -coda wavetrains clearly dominate the far-regional seismic records. The later part of an Lg -coda wavefield is generally expected to consist of omnidirectional and multiple scattered waves; still, in the present study, preferential propagation directions of scattered waves are identified in seismic signals, even for a lapse time larger than 1200 s. The comparison of the Lg -coda characteristics for two different groups of earthquakes and for the different arrays shows that the geometrical configuration of the event array strongly influences the back-azimuthal distribution of detected waves. More precisely, temporal variations of the Lg -coda characteristics are identified: (1) as a transitory regime in the early part of the coda where arrival directions deviate from the epicenter back azimuth (eastward or westward); (2) as a final regime where the later part of the Lg coda observed by the two northern arrays exhibits incoherent phases with random propagation directions; and (3) as a final regime for the three southern arrays, which reveals coherent arrivals propagating from array-specific back azimuths not related to the epicenter back azimuth. Electronic Supplement: Figures showing frequency content of detections.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America (SSA)
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